Various methods for production of amine products have been proposed and a number of them have been commercially utilized. The present invention concerns the production of lower alkylamines by the catalytic amination of lower aliphatic alkane derivatives such as mono- and polyhydric alcohols, alcoholamines, and compounds from which these alcohols are derived, including epoxides, ketones, alkyleneamines and alkylenimines.
The catalytic amination of alcohols or amines is a process which has been long recognized in the prior art. It generally concerns the reaction of an alcohol or an amine with ammonia or a primary or secondary amine in the presence of a hydrogenation catalyst and usually in the presence of hydrogen.
The most difficult problem in the manufacture of amines by this and other proposed processes is that the chemical synthesis reactions used also form substantial amounts of by-products, which are of considerably less value and as a result often render the synthesis inefficient and not commercially feasible.
The most desirable amine products generally are those products wherein an amine group replaces the non-amine functional group or groups in the alkyl starting material without any further modification of the starting material. Most heavier, more highly substituted amines and heterocyclic nitrogen compounds can be further synthesized from these preferred alkylamines. A synthesis of these heavier, substituted and heterocyclic amines directly from the alkyl starting materials usually yields other unwanted by-products.
The amine products produced in accordance with the present invention have many uses. In addition to their use as intermediates for synthesizing other chemical materials, they are utilized, for example, in fungicides and insecticides.
For convenience in the description of the invention hereinbelow, the amination of ethylene glycol and monoethanolamine to ethylenediamine and other products will be most comprehensively discussed, although the present invention is not limited to these starting materials.
In the amination of ethylene glycol, the primary products usually are monoethanolamine (MEA), ethylenediamine (EDA), and piperazine [also termed diethylenediamine (DEDA)] and aminoethylethanolamine, (AEEA).
Numerous other chemical reactions are known for producing alkylamines. For example, in the synthesis of ethylenediamine, the following reactions have been proposed: the hydrolysis of ethylene urea; reductive amination of formaldehyde cyanohydrin; the reduction of cyanogen; the reduction of 1,2-dinitroethane; and the amination of chloroacetylchloride followed by reduction. None of these chemical processes appear to have been operated on a commercial scale because of the process requirements and costs of raw materials.
One of the most widely used commercial processes for producing ethylenediamine today involves a reaction of ethylenedichloride with aqueous ammonia. The ethylenedichloride is reacted with aqueous 30 to 40% ammonia to produce a dilute aqueous solution of amines. Sodium hydroxide is then added to neutralize the hydrochloric acid formed in the ammonia-ethylene dichloride reaction. This neutralization step forms additional water and gives rise to by-product sodium chloride. An illustration of the approximate distribution or profile of products produced by such a process is as follows:
______________________________________ Products Wt. % of Production ______________________________________ Ethylenediamine (EDA) 41% Diethylenetriamine (DETA) 25% Triethylenetetramine (TETA) 10% Tetraethylenepentamine (TEPA) 8% Pentaethylenehexamine (PEHA) 13% Polyamine Heavies (PAH) 13% Piperazine (DEDA) 1.5% Aminoethylpiperazine (AEP) 1.5% ______________________________________
About 2.5 lbs. of sodium chloride is produced per lb. of the amines produced.
Although the product distribution is commercially feasible, the presence of chlorine in the system, including in the corrosive form of hydrogen chloride, causes expensive maintenance costs. Moreover, recovery of the desired amine products from the salt-containing aqueous solutions is difficult and the disposal of the large quantities of salt is an ever increasing environmental problem. The cost of the starting materials also has been a discouraging factor.
A method which has recently emerged commercially is the reduction of amino acetonitrile to form ethylenediamine. Although this process, according to the literature can be operated to produce as much as 90% ethylenediamine in the amine yield, the expense of the starting materials in the process and other economic considerations do not make this process commercially attractive.
As indicated above, the catalytic amination of alkane derivatives including aliphatic alcohols, aminoalcohols or amines has been the subject of much investigation. It should be noted that there are numerous materials which have the ability to catalyze such amination processes, but the mere ability to catalyze is far from sufficient to term a catalyst of commercial significance.
U.S. Pat. No. 2,861,995 describes a method of converting ethanolamine to various nitrogen-containing products by using a metal hydrogenation catalyst comprising nickel, cobalt, copper chromite, catalytic noble metal such as platinum and palladium, and Raney nickel and Raney cobalt. They may be supported on a carrier such as alumina.
U.S. Pat. No. 3,068,290 describes a process for converting ethanolamine to ethylenediamine by using a hydrogenation catalyst, such as described above, in a reaction which is in the liquid phase, under autogenous pressure. The patent also describes a preferred catalyst which is a combination of nickel and magnesium oxides (Ni--MgO), obtained by thermal decomposition of coprecipitated nickel and magnesium formates or oxalates.
U.S. Pat. No. 3,137,730 describes the conversion of ethylene glycol by using a supported catalyst comprising nickel and copper. U.S. Pat. No. 3,270,059 teaches an amination process in the presence of a supported catalyst which is produced by sintering oxygen compounds of either nickel or cobalt at temperatures in excess of 700.degree. C. and reducing the sintered metal compound by treatment with hydrogen. U.S. Pat. No. 3,766,184 describes a catalyst containing iron with either nickel, cobalt or mixtures thereof. Ruthenium catalysts are also referred to in this and other patents as useful in amination processes for producing aliphatic amines, e.g., see U.S. Pat. No. 2,754,330.
U.S. Pat. No. 4,209,424 discloses an amination catalyst which is stabilized with a sodium component. Example 18 of that patent pertains to a nickel, sodium and rhodium-containing catalyst, and the patentees concluded that the activity of the catalyst in the amination of ethanolamine was high due to the presence of the rhodium.
U.S. Pat. No. 4,123,462, herein incorporated by reference, discloses catalysts containing nickel and rhenium, supported on a material selected from .alpha.-aluminas, silica, silica-aluminas, silica-titanias, and kieselguhrs, or diatomaceous earths which have improved properties over those catalysts heretofore known for catalyzing the amination of aliphatic lower alkyl derivatives. Examples 9 to 12 of that patent relate to nickel-palladium catalysts. In general, these catalysts are inferior to nickel-rhenium catalysts and exhibit no clear benefit over the use of nickel alone.
Modern commercial catalytic processes require catalysts to be more than active, i.e., yield high conversions in the chemical reactions they catalyze. In the case of amination processes where numerous competing reactions occur yielding many by-products, it is important for the catalyst to have good selectivity or the ability to afford a high yield of useful product with a concomitant small yield of undesired product. The optimum reaction conditions including temperaure, pressure and relative proportions of reactants, as well as reaction time, may be determined by the catalyst, and in so doing may affect the economics of the whole process. The cost of the catalyst, its method of preparation and its effective life as well as its physical properties may be determinative of a successful, viable process.
British patent application No. 2,121,697 discloses a hydrogenation catalyst of a Raney catalyst, e.g., nickel, cobalt, chromium, copper and/or iron optionally modified with molybdenum, chromium, iron, nickel, cobalt, zirconium, copper, silver or platinum group metal, which is mixed with a nitrile and surfactant to reduce its pyrophoric properties.